Synthetic polymers are used in very numerous industrial fields, particularly in the packaging field, because they exhibit at least the following three advantages:                easily molded,        very good physicochemical properties,        low cost.But the principal disadvantage of these materials is that they can not be biodegraded, after use, via natural and ecological pathways. Plastic waste products thus become very major polluting agents. The only principal approaches employed today are recycling and incineration. But this only represents a small volume and generates very high costs.        
Biodegradability can be defined as the physical and/or chemical degradation at the molecular level of the substances by the action of environmental factors (particularly the enzymes stemming from the metabolic processes of microorganisms.)
Known in the prior art are biodegradable materials that can be substituted for synthetic plastic materials.
First of all, one can cite the biodegradable materials stemming from a mixture of a polymer and a surface-modified starch described, for example, in U.S. Pat. Nos. 1,485,833, 1,487,050, 4,021,388 and 4,125,495 and European Patent No. 45 621. This chemical modification of the surface state of the starch enables creation of ether or ester functions or making the surface of the starch hydrophobic.
It has also been proposed to use materials formed by a polymer and a destructured starch, i.e., a starch having been subjected to a specific pretreatment by a destructuring agent such as urea, the hydroxides of alkali metals or alkaline-earth metals, as described in European Patent Nos. 437 589,437 561 and 758 669, or by water as described in U.S. Pat. No. 5,095,054. The invention described in European Patent No. 535 994 does not employ the term destructured starch, but rather the term gelatinized in that the starch is heated at 40° C. in the presence of water, from 1 to 45% by weight, for a sufficiently long period of time to cause the starch granules to burst.
Methods for producing biodegradable materials constituted of starch, polymers other than propylene and additives have also been described. These additives can be unsaturated chemical compounds such as natural rubber or elastomers as described in European Patent No. 363 383, or plant materials such as wood flour or cellulose as described in European Patent No.652 910, or a plasticizer such as the polyols, glycerol, calcium chloride or ethers as described in European Patent Nos. 473 726 and 575 349, and U.S. Pat. No. 5,393,804. Among the envisaged polymers, one can cite poly(ethylene/vinyl alcohol) and poly(ethylene/acrylic acid) proposed in European Patent Nos. 400 532, 413 798 and 436 689, or aliphatic copolymers and polyesters as proposed in European Patent No. 539 541, or low-density polyethylene as proposed in PCT Patent Application No. WO 91/15542 and U.S. Pat. No. 5,162,392. Finally, European Patent No. 560 244 proposes the use of starch with at least 80% by weight of amylopectin, whereas in our case amylopectin represents a maximum of 73% of the starch present in the flours used.
Finally, it has been envisaged to prepare biodegradable materials from starch mixed with polymers that have been chemically modified so as to be able to react with the hydroxyl groups of the starch and thereby create bonds between the polymer and the starch. These techniques are described, for example, in European Patent Nos. 554 939 and 640 110.